Along with the Strait of Hormuz in the Persian Gulf near Iran and Oman, the Strait of Malacca is the worldâ€™s most important shipping chokepoint.

Linking the Indian Ocean to the South China Sea and Pacific Ocean, the Malacca Strait is by far the shortest maritime route connecting Persian Gulf energy producers to their largest consumers in countries like China, Japan, and South Korea.

50,000 merchant ships carrying 40 percent of all world trade pass through the 900-km long (550 miles) strait each year. Itâ€™s particularly strategic for regional energy supplies. According to the U.S. governmentâ€™s Energy Information Agency (EIA), in 1993 about 7 million barrels per day (bbl/d) of oil and petroleum productsâ€”at the time about 20 percent of global seaborne traded oilâ€” transited the Strait of Malacca. By 2011, this number had risen to 15 million bbl/d or 33 percent of all seaborne traded oil.

Northeast Asiaâ€™s dependence on oil coming through the strait is remarkable. Japan relies on the Malaccan Strait for about 90 percent of its oil imports. As recently as 2010, China relied on the strait for some 80 percent of its imported oil. Little wonder then that former President Hu Jintao famously referred to Chinaâ€™s Malacca Dilemma.

Three nationsâ€”Singapore, Malaysia, and Indonesiaâ€” sit atop the Malaccan Strait, which is just 1.7 miles (2.7 km) wide at its narrowest point. While foreign navies like the United States have traditionally operated in the area, and Chinaâ€™s navy has increasingly taken a strong interest in doing so, the naval forces of these littoral states should not be overlooked.

Indeed, taking stock of their strategic location, all three countries have acquired submarine forces, with Indonesia in particular possessing considerable subsurface ambitions for the future.

The Republic of Singaporeâ€™s Navy (RSN) has one of the most formidable submarine forces in the region, commissioning its sixth vessel in May. All six of the vessels were purchased from Sweden in two different batches.

Four of Singaporeâ€™s submarines are of the Challenger-class variant. Purchased from Sweden in the 1990s and delivered between 1995-1997, the Challenger-class submarines displace 1,200 tons when submerged and can travel about 20 knots underwater. Each unit has 6 torpedo tubes and carries about 10 of Swedenâ€™s Type 613 torpedoes and 4 of Swedenâ€™s Type 431 torpedoes.

With these submarines ageing, Singapore again turned to Sweden for its underwater capabilities, agreeing to purchase two Archer-class submarines in 2005.The Archer-class vessels are highly upgraded versions of the VÃ¤stergÃ¶tland Class diesel-electric submarines Sweden has long operated. Notably, the Archer-class vessels have air independent propulsion (AIP) systems, allowing them to operate quietly and remain submerged for weeks. They also have 9 torpedo tubes and carry 12 Black Shark heavy torpedoes, 6 type 431/451 light torpedoes, as well as mines.

Singaporeâ€™s traditional rival, Malaysia, has an enormous coastline and is also located along the strategic Strait of Malacca. These factors led the Royal Malaysian Navy (RMN) to determine in 2002 that it would need a small submarine force to patrol its waters.

â€œWe have such a large body of water to police. We need submarines because it is a force multiplier. They can appear anywhere and because they are stealth, they are hard to detect. That makes our deterrent value much higher,â€ Malaysian Defense Minister Najib Razak explained at the time.

Towards that end, Malaysia turned to France to service its underwater needs, agreeing to purchase two Scorpene-class submarines (the same kind India is now buying from France) and a refitted French submarine for training purchases. The deal was worth 1.035 billion euro at the time, which is today around US$1.3 billion. Both of the Scorpene-class vessels were commissioned in 2009. Malaysiaâ€™s version of the submarines does not include AIP but they do have the ability to launch EXOCET SM39 anti-ship missiles with a range of 50 km while submerged.

Malaysiaâ€™s decision to acquire the Scorpene-class submarines has heightened Indonesiaâ€™s insecurity, causing it to reexamine its own submarine fleet.

As the worldâ€™s largest archipelagic country, Indonesia has coastlines stretching 108,000 km and claims an exclusive economic zone (EEZ) of around 5.8 million square km. It also sits along at least three major maritime shipping lanes, the Malacca, Sunda and Lombok Straits.

Not surprisingly, then, Indonesiaâ€™s Navy, Tentara Nasional Indonesia-Angkatan Laut (TNIâ€“AL), has long seen it fit to operate an underwater force. Since the early 1980s, TNI-AL has operated two submarines, the KRI Cakra and KRI Nenggala, which are U-209/1300 submarines acquired from Germany. Called Cakra-class submarines in Indonesia, both vessels were refitted extensively by a South Korean company in the last decade, which resulted in the modernization of their â€œpropulsions systems, detection and navigation systems, and new fire control and combat systems,â€ according to Nuclear Threat Initiative.

More importantly, Indonesia has signaled it has ambitious plans to expand its underwater fleet, with naval officials at times suggesting the country would like to ultimately acquire between 14 and 18 submarines. Indonesiaâ€™s Defense Strategic Plan of 2024 called for TNI-AL to acquire at least ten submarines by that time, although many believe financial constraints will make this goal unattainable.

These great ambitions are partly driven by history, Koh Swee Lean Collin, an Associate Research Fellow at the RSIS Military Studies Program, tells The Diplomat.

â€œDuring its 'golden age' in the 1960s, the TNI-AL had up to 12 Soviet-built submarines of the 'Whiskey class.â€™â€ Colin explains, while noting that financial constraints may limit the navy to eight vessels for now.

Nonetheless, Indonesia is pushing ahead with this slightly pared back goal.

After entertaining bids from Russian, Turkish and French companies, among others, in December 2011 Indonesia ultimately decided to purchase 3 new submarines from South Koreaâ€™s Daewoo Shipbuilding and Marine Engineering, the company that refitted the TNI-ALâ€™s existing submarine fleet. The submarines are reportedly of the Type-209/1400 diesel-electric variant, and have been described by Indonesian officials as similar to Malaysiaâ€™s Scorpene-class. The contract was worth US$1.1 billion, the submarines expected to be delivered between 2015-2018.

Under the terms of the contract, the third submarine will be built in Indonesia, reflecting Indonesiaâ€™s goal of acquiring the capability to produce submarines indigenously. Indeed, just last month Defense Minister Purnomo Yusgiantoro reaffirmed that the country is building the necessary infrastructure to produce submarines domestically.

Indonesia also recently completed a new military base on Palu Bay, which will serve as the countryâ€™s submarine base. The base took two years to build and cost US$717,000, according to Jakarta Post. The newspaper also said that Palu Bay is â€œ10 kilometers wide and its coastline stretches for 68 kilometers while its depth reaches 400 meters.â€

Collin, the researcher at RSIS, explains it this way:

â€œThe primary reasons for selecting Palu have surely got to do with geography. It's located first of all astride the Strait of Makassar and the Palu Bay is a narrow, deep inlet (reportedly 400m) which provides maximum security for the submarine force in terms of concealment and defense against attacks. Besides its sitting astride the strategic waterway, Palu offers direct access northwards into the Sulawesi Sea, where Indonesia still has outstanding dispute with Malaysia over the Ambalat offshore oil block.â€

Overall, Collin describes the purpose of Indonesiaâ€™s submarine fleet as one of deterrence in peacetime, and sea-control or at least sea-denial in times of war.

â€œSubmarines certainly form a major facet of the whole game planâ€ of Indonesiaâ€™s Navy, he says. â€œTheir role is intended largely in peacetime to constitute a 'fleet-in-being' deterrent to any potential foe. In wartime, due to the multiplicity of possible sea approaches the adversary may undertake, it is necessary to carry out effective sea denial using submarines, by focusing them on the strategic SLOCs of the highest priority.â€

Owing to its geography, â€œPalu base certainly serves as a 'force multiplier' in this respect,â€ Collin adds.

Singaporeâ€™s traditional rival, Malaysia, has an enormous coastline and is also located along the strategic Strait of Malacca. These factors led the Royal Malaysian Navy (RMN) to determine in 2002 that it would need a small submarine force to patrol its waters.

â€œWe have such a large body of water to police. We need submarines because it is a force multiplier. They can appear anywhere and because they are stealth, they are hard to detect. That makes our deterrent value much higher,â€ Malaysian Defense Minister Najib Razak explained at the time.

Towards that end, Malaysia turned to France to service its underwater needs, agreeing to purchase two Scorpene-class submarines (the same kind India is now buying from France) and a refitted French submarine for training purchases. The deal was worth 1.035 billion euro at the time, which is today around US$1.3 billion. Both of the Scorpene-class vessels were commissioned in 2009. Malaysiaâ€™s version of the submarines does not include AIP but they do have the ability to launch EXOCET SM39 anti-ship missiles with a range of 50 km while submerged.

Malaysiaâ€™s decision to acquire the Scorpene-class submarines has heightened Indonesiaâ€™s insecurity, causing it to reexamine its own submarine fleet.

On December 16, according to The Jakarta Post, Ade Supandi, the chief of staff of the Indonesian navy (TNI-AL), clarified that while Jakarta had decided to buy diesel submarines, it is still currently reviewing three types of submarines from three countries: Russia, South Korea, and Germany.

“The Navy and the military headquarters are still conducting a strategic review of the matter,” Supandi said Tuesday.

Indonesia has a record of purchasing submarines from all three countries. The relationship with Russia dates back the furthest, with 12 Whiskey-class submarines purchased from the Soviet Union during the Cold War. Those subs were gradually decommissioned – the last in 1990. And as mentioned earlier, Indonesia currently operates two German-built Type 209 submarines – which are expected to be decommissioned by 2020 – and has ordered three Chang Bogo-class submarines from South Korea. In addition to the three candidates, Indonesia also reportedly had government-to-government talks with France earlier this year regarding theScorpene-class 1000 diesel-electric attack submarines.

Supandi’s comments suggest that key specifics are still yet to be publicly revealed on the submarine purchase. As I wrote back in September, while navy spokesman Comr. Zainuddin had said then that Indonesia may buy Russian submarines, he also had declined to mention key details like which specific submarine type would be purchased and how it would be financed.

The financing point is critical because Indonesia has been struggling to boost its defense budget amid financial troubles in 2015 (See: “Will Indonesia’s Military Budget Fall or Rise?”). Supandi himself reiterated that point when he said that the decision regarding which submarines to purchase would be based on the current state of the budget situation. He also added that procurement would take time as it would have to go through three stages: drawing up submarine specifications; planning the budget; and then building the vessels.